There are several prior art methods which target individual use cases (e.g., overlay metrology, pattern placement metrology, and critical dimension (CD) metrology).
Overlay metrology is mainly based on optical imaging or scatterometry. The ARCHER series of KLA-Tencor Corporation can be used for the optical overlay control. The mechanical, electrical, and optical set-up of the products of the ARCHER series are incorporated herein by reference in their entirety.
Pattern placement metrology is typically used on reticles only, thereby combining accurate stage position metrology and optical imaging. Pattern placement metrology can be carried out by the IPRO series of KLA-Tencor Corporation. The mechanical, electrical, and optical set-up of the products of the IPRO series are incorporated herein by reference in their entirety.
CD metrology may for example be carried out with a scanning electron microscope (SEM) in on-target and device pattern SEM imaging. CD metrology may for example also be performed with KLA-Tencor's IPRO metrology tool.
The TERON Series of KLA-Tencor Corporation provide 193 nm-wavelength reticle inspection systems. The TERON Series is designed for photomask defect inspection of optical and EUV reticles during both development and production. The products of the TERON series are incorporated herein by reference in their entirety.
International patent application PCT/US13/69138 with the international filing date of Sep. 24, 2013, describes a method and system for performing model-based registration and critical dimension measurement. At least one simulated image of the measurement site is generated. At least one parameter of the computer model is adjusted to minimize dissimilarities between the simulated images and the optical images. The pattern registration parameter or the critical dimension parameter of the computer model are reported when dissimilarities between the simulated images and the optical images are minimized.
U.S. Pat. No. 8,248,618 which issued on Aug. 21, 2012 and is incorporated by reference herein, describes one example for the pattern placement metrology. The method is suitable for reticles only and combines accurate stage position metrology and optical imaging. The method is implemented in a metrology tool comprising a measurement table which is movable in X-coordinate direction and Y-coordinate direction. A first intensity profile is recorded along a first measurement direction, which is parallel to the X-coordinate direction. A second intensity profile is recorded along a second measurement direction, which is parallel to the Y-coordinate direction. A two-dimensional position of a center of gravity with respect to the coordinate system of the metrology tool is determined from the first intensity profile and the second intensity profile.
U.S. Pat. No. 7,675,633, which issued on Mar. 9, 2010 and is incorporated by reference herein, describes one possible method for CD metrology. The measuring method is used for measuring at least one structure on the substrate, wherein the measuring includes the position and/or the width of the structure.
Additionally, several other US patents, like U.S. Pat. No. 8,582,113, U.S. Pat. No. 8,352,886, or U.S. Pat. No. 7,823,295, disclose devices or methods for determining the positions of structures on a mask.
The prior art methods use rather static approaches. Optical imaging is limited in resolution. On-device pattern CD and registration metrology is a big challenge due to missing contrast at specific small feature sizes. CD-SEM metrology uses an electron beam directed at a location to be measured. Charging and damage effects may occur that can affect the pattern physically or lead to inaccurate metrology.